1. Field of the Invention
This invention relates to a method of preparation of benzyl alcohols or ring substituted benzyl alcohols by decarbonylation of formic acid esters of benzyl alcohol or ring substituted benzyl alcohols. More especially, this invention relates to such a decarbonylation carried out in the presence of a catalyst to provide benzyl alcohols or ring substituted benzyl alcohols with a high volume/time yield.
2. Discussion of the Prior Art
Benzyl alcohols are valuable starting compounds for the preparation of aromatic aldehydes.
Hydroxymethylbenzyl alcohols (xylylene glycols) are valuable intermediates in organic syntheses and also are used in the preparation of polyesters and polyurethanes.
It is known that ethyl formiate is cleaved in the presence of sodium alcoholate to ethanol and carbon monoxide (Chem. Zentralblatt 39 [1868] 632; Journ. Amer. Chem. Soc. 50 [1928] 235; Berichte 65 [1932] 954). It is disadvantageous, however, that the transformation is poor and large amounts of sodium alcoholate are required for the cleavage.
Other strong bases, such as sodium hydride, potassium tert.-butylate and triphenyl methyl sodium have been used for the decarbonylation of ethyl formiate and butyl formiate (Journ. Org. Chem. 31 [1966] 2623). By this method high transformations of the formic acid esters are achieved, but it is difficult to perform, and it is also uneconomical. For example, stoichiometric amounts of the very expensive bases are required. In the decarbonylation, the reaction products are first the metal salts of the alcohols, and the alcohols have to be released from them by hydrolysis and isolated by extraction from aqueous solution.
It is also known to cleave phenyl formiate, in the presence of stoichiometric amounts of sodium amide, to sodium phenolate, carbon monoxide and ammonia. This method also has the disadvantage that it is technically complicated and uneconomical, since large amounts of sodium amide must be used, and the phenol has to be released from its sodium salt (Comptes Rendus 178 [1924] 1583).
Methods have also become known for the decarbonylation for formic acid esters of aliphatic alcohols by the use of hydrogenation catalysts to form alcohols. For example, in German Pat. No. 1,805,403, there is described a method for the decarbonylation of formic acid esters of aliphatic alcohols having a carbon number of 1 to 9 on copper-nickel mixed catalysts; it is, however, a decided disadvantage that the decarbonylation is not selective and, in addition to the alcohols, the corresponding aldehydes form as accompanying products, and are very difficult to separate from the alcohols.
On the other hand, it is known that n-octyl formiate can be cleaved to octanol and carbon monoxide with a high yield in the presence of palladium-carbon catalysts (Journ. Org. Chem. 35 [1970] 1694). This method of decarbonylation, however, fails completely in the case of the araliphatic formic acid ester benzyl formiate, which is cleaved in a virtually quantitative manner to toluene and carbon dioxide on the same catalyst.